The surface of a pressure-sensitive adhesive tape to be used in the dicing of a semiconductor opposite to its surface closely adhering to a wafer needs to be fixed to a base for fixing the wafer at the time of the dicing. In general, such fixation is performed with the negative pressure of vacuum adsorption or the like.
When such fixation with the negative pressure is performed, the pressure-sensitive adhesive tape may closely adhere to the base in an excessive manner owing to a state where the negative pressure is excessively applied or to the melting of the pressure-sensitive adhesive tape caused by heat generation at the time of the dicing. When such excessive close adhesion occurs, handleability upon release of the fixation to the base deteriorates, and for example, the following problem arises. A semiconductor production process including the dicing does not proceed smoothly.
The following technology has been reported for solving such problem of the excessive close adhesion (Patent Literature 1). In a wafer surface protective tape formed of two layers, i.e., a base material film and a pressure-sensitive adhesive layer, a center line surface roughness Ra of the surface of the base material film opposite to the pressure-sensitive adhesive layer is controlled to a predetermined size.
However, the base material film of the pressure-sensitive adhesive tape to be used in the dicing of the semiconductor is required to have an expanding (stretching) characteristic and level difference-following characteristic peculiar to the semiconductor production process. That is, the base material film of the pressure-sensitive adhesive tape to be used in the dicing of the semiconductor needs to be capable of satisfactorily stretching in an expanding step and needs to follow the level difference of the semiconductor satisfactorily. A base material film formed of a material having a large elongation percentage is selected as a base material film that can respond to such requirements. However, the surface state of such base material film is susceptible to temperatures. Accordingly, the following problem arises. Even when the center line surface roughness Ra of the surface of the base material film is controlled to a predetermined size as reported in Patent Literature 1, the center line surface roughness Ra controlled to the predetermined size largely changes owing to a change in air temperature or a change in temperature of a processing apparatus, and hence an effect of the invention described in Patent Literature 1 cannot be expressed.
For example, at the time of the dicing, in particular, at the time of laser dicing, the wafer generates heat owing to energy produced by laser processing. When the wafer generates heat as described above, the following problem arises. Even when the center line surface roughness Ra of the surface of the base material film is controlled to a predetermined size as reported in Patent Literature 1, such problem of the excessive close adhesion as described above cannot be solved but instead the excessive close adhesion is accelerated.
In addition, in recent years, the size of the wafer to be used in the dicing of the semiconductor has been enlarging and hence a time period for the dicing has been lengthening. As a result, the quantity of heat to be generated by the wafer increases and hence the problem becomes additionally remarkable.
Particularly in LED dicing out of various kinds of semiconductor dicing, a semiconductor wafer to be used is constituted of an extremely brittle material such as gallium nitride, gallium arsenide, or silicon carbide. Accordingly, the base material film of the pressure-sensitive adhesive tape is required to have additionally high levels of the expanding (stretching) characteristic and level difference-following characteristic for preventing the breakage of the semiconductor wafer. Accordingly, the problem becomes additionally remarkable in the pressure-sensitive adhesive tape to be used in the LED dicing.
On the other hand, the surface of the film is generally smooth, and when such film is processed into a roll shape, a phenomenon in which different portions of the film are brought into contact with each other to closely adhere to each other, that is, blocking occurs. The roll in which the blocking has occurred may cause, for example, the following inconvenience. The operation of unwinding the film becomes difficult. In particular, a film having a large elongation percentage generally has a plasticizer added thereto. In such film, an adverse effect caused by the blocking becomes remarkable because a slight gap between the contacting portions of the film is filled by the deposition of the plasticizer on the surface of the film. When the surface of the film is subjected to pressure-sensitive adhesive processing with a pressure-sensitive adhesive, the adverse effect of the blocking becomes additionally large because the pressure-sensitive adhesive itself has adhesiveness.
When the roll-shaped film in which the blocking has occurred is unwound, extra force for releasing the close adhesion between the contacting portions of the film is needed. When such extra force is applied, the film elongates to deform, or even in the case where the film does not deform, the force is accumulated as stress strain. When the film that has deformed owing to such cause as described above is applied to the pressure-sensitive adhesive tape, it becomes difficult to attach the tape while following an adherend. In addition, when the film in which the stress strain has been accumulated by such cause as described above is applied to the pressure-sensitive adhesive tape, the adherend may break owing to the occurrence of natural release of the stress strain after the tape has been attached to the adherend.
When the pressure-sensitive adhesive tape is used in semiconductor processing, a semiconductor wafer as an adherend is brittle or liable to chip because the semiconductor wafer is constituted of a brittle material. Accordingly, when the film that has deformed owing to such cause as described above is applied to the pressure-sensitive adhesive tape, it becomes difficult to attach the tape while following a fine and intricate circuit pattern of the semiconductor wafer. In addition, when the film in which the stress strain has been accumulated by such cause as described above is applied to the pressure-sensitive adhesive tape, the semiconductor wafer easily breaks owing to the occurrence of natural release of the stress strain after the tape has been attached to the semiconductor wafer.
In particular, a wafer to be used in an LED is constituted of an extremely brittle material such as gallium nitride, gallium arsenide, or silicon carbide. Accordingly, the prevention of the blocking in the pressure-sensitive adhesive tape to be used in the LED dicing or the like is of particular importance.
Conventional technologies for preventing the blocking are roughly classified into two technologies.
One conventional technology is to subject the back surface of a film to a physical treatment such as embossing (Patent Literature 2). However, the technology involves the following problem. Unevenness formed on the back surface of the film serves as a stress concentration structure, and hence when the film is unwound from a roll shape, the film tears or breaks owing to the force of the unwinding with the unevenness as a starting point.
The other conventional technology is to apply a silicone release agent to the back surface of the film (Patent Literature 3). However, the technology involves the following problem. The silicone release agent hardly conforms to the back surface of the film because its chemical affinity for the back surface of the film is low owing to its surface tension. In addition, in the case where the film having the silicone release agent applied to its back surface is applied to the pressure-sensitive adhesive tape, the following problem may arise. When the stretching of the pressure-sensitive adhesive tape such as expanding is performed, a layer treated with the silicone release agent may be unable to follow the stretching and hence the treated layer is crushed to cause contamination. Although a technology involving applying a cross-linked silicone release agent is available for improving the chemical affinity of the silicone release agent for the back surface of the film, a cross-linked silicone generally has an extremely small elongation percentage, and hence in the case where the film having the cross-linked silicone release agent applied to its back surface is applied to the pressure-sensitive adhesive tape, the following problem arises. When the stretching of the pressure-sensitive adhesive tape such as expanding is performed, a layer treated with the cross-linked silicone release agent cannot follow the stretching and hence anchoring property cannot be maintained.